In this 13th installment of the 1st Godzilla series deals with the underground country of Seatopia striking back at mankind. The reason? A third of their country has already been destroyed, due to underground nuclear tests. They send their guardian, Megalon, to destroy the surface world. They also request the aid from Nebula M Space Hunter to send their monster, Gigan, to help Megalomaniac destroy the surface world. Can these two menacing monsters be stopped? Is the surface world doomed?